arch/arm64/kernel/ftrace.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * arch/arm64/kernel/ftrace.c
  *
  * Copyright (C) 2013 Linaro Limited
  * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
  */

 #include <linux/ftrace.h>
 #include <linux/module.h>
 #include <linux/swab.h>
 #include <linux/uaccess.h>

 #include <asm/cacheflush.h>
 #include <asm/debug-monitors.h>
 #include <asm/ftrace.h>
 #include <asm/insn.h>
 #include <asm/patching.h>

 #ifdef CONFIG_DYNAMIC_FTRACE
 /*
  * Replace a single instruction, which may be a branch or NOP.
  * If @validate == true, a replaced instruction is checked against 'old'.
  */
 static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
 			      bool validate)
 {
 	u32 replaced;

 	/*
 	 * Note:
 	 * We are paranoid about modifying text, as if a bug were to happen, it
 	 * could cause us to read or write to someplace that could cause harm.
 	 * Carefully read and modify the code with aarch64_insn_*() which uses
 	 * probe_kernel_*(), and make sure what we read is what we expected it
 	 * to be before modifying it.
 	 */
 	if (validate) {
 		if (aarch64_insn_read((void *)pc, &replaced))
 			return -EFAULT;

 		if (replaced != old)
 			return -EINVAL;
 	}
 	if (aarch64_insn_patch_text_nosync((void *)pc, new))
 		return -EPERM;

 	return 0;
 }

 /*
  * Replace tracer function in ftrace_caller()
  */
 int ftrace_update_ftrace_func(ftrace_func_t func)
 {
 	unsigned long pc;
 	u32 new;

 	pc = (unsigned long)ftrace_call;
 	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
 					  AARCH64_INSN_BRANCH_LINK);

 	return ftrace_modify_code(pc, 0, new, false);
 }

 static struct plt_entry *get_ftrace_plt(struct module *mod, unsigned long addr)
 {
 #ifdef CONFIG_ARM64_MODULE_PLTS
 	struct plt_entry *plt = mod->arch.ftrace_trampolines;

 	if (addr == FTRACE_ADDR)
 		return &plt[FTRACE_PLT_IDX];
 	if (addr == FTRACE_REGS_ADDR &&
 	    IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
 		return &plt[FTRACE_REGS_PLT_IDX];
 #endif
 	return NULL;
 }

 /*
  * Find the address the callsite must branch to in order to reach '*addr'.
  *
  * Due to the limited range of 'BL' instructions, modules may be placed too far
  * away to branch directly and must use a PLT.
  *
  * Returns true when '*addr' contains a reachable target address, or has been
  * modified to contain a PLT address. Returns false otherwise.
  */
 static bool ftrace_find_callable_addr(struct dyn_ftrace *rec,
 				      struct module *mod,
 				      unsigned long *addr)
 {
 	unsigned long pc = rec->ip;
 	long offset = (long)*addr - (long)pc;
 	struct plt_entry *plt;

 	/*
 	 * When the target is within range of the 'BL' instruction, use 'addr'
 	 * as-is and branch to that directly.
 	 */
 	if (offset >= -SZ_128M && offset < SZ_128M)
 		return true;

 	/*
 	 * When the target is outside of the range of a 'BL' instruction, we
 	 * must use a PLT to reach it. We can only place PLTs for modules, and
 	 * only when module PLT support is built-in.
 	 */
 	if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
 		return false;

 	/*
 	 * 'mod' is only set at module load time, but if we end up
 	 * dealing with an out-of-range condition, we can assume it
 	 * is due to a module being loaded far away from the kernel.
 	 *
 	 * NOTE: __module_text_address() must be called with preemption
 	 * disabled, but we can rely on ftrace_lock to ensure that 'mod'
 	 * retains its validity throughout the remainder of this code.
 	 */
 	if (!mod) {
 		preempt_disable();
 		mod = __module_text_address(pc);
 		preempt_enable();
 	}

 	if (WARN_ON(!mod))
 		return false;

 	plt = get_ftrace_plt(mod, *addr);
 	if (!plt) {
 		pr_err("ftrace: no module PLT for %ps\n", (void *)*addr);
 		return false;
 	}

 	*addr = (unsigned long)plt;
 	return true;
 }

 /*
  * Turn on the call to ftrace_caller() in instrumented function
  */
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned long pc = rec->ip;
 	u32 old, new;

 	if (!ftrace_find_callable_addr(rec, NULL, &addr))
 		return -EINVAL;

 	old = aarch64_insn_gen_nop();
 	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

 	return ftrace_modify_code(pc, old, new, true);
 }

 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
 			unsigned long addr)
 {
 	unsigned long pc = rec->ip;
 	u32 old, new;

 	if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
 		return -EINVAL;
 	if (!ftrace_find_callable_addr(rec, NULL, &addr))
 		return -EINVAL;

 	old = aarch64_insn_gen_branch_imm(pc, old_addr,
 					  AARCH64_INSN_BRANCH_LINK);
 	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

 	return ftrace_modify_code(pc, old, new, true);
 }

 /*
  * The compiler has inserted two NOPs before the regular function prologue.
  * All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are live,
  * and x9-x18 are free for our use.
  *
  * At runtime we want to be able to swing a single NOP <-> BL to enable or
  * disable the ftrace call. The BL requires us to save the original LR value,
  * so here we insert a <MOV X9, LR> over the first NOP so the instructions
  * before the regular prologue are:
  *
  * | Compiled | Disabled   | Enabled    |
  * +----------+------------+------------+
  * | NOP      | MOV X9, LR | MOV X9, LR |
  * | NOP      | NOP        | BL <entry> |
  *
  * The LR value will be recovered by ftrace_regs_entry, and restored into LR
  * before returning to the regular function prologue. When a function is not
  * being traced, the MOV is not harmful given x9 is not live per the AAPCS.
  *
  * Note: ftrace_process_locs() has pre-adjusted rec->ip to be the address of
  * the BL.
  */
 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
 {
 	unsigned long pc = rec->ip - AARCH64_INSN_SIZE;
 	u32 old, new;

 	old = aarch64_insn_gen_nop();
 	new = aarch64_insn_gen_move_reg(AARCH64_INSN_REG_9,
 					AARCH64_INSN_REG_LR,
 					AARCH64_INSN_VARIANT_64BIT);
 	return ftrace_modify_code(pc, old, new, true);
 }
 #endif

 /*
  * Turn off the call to ftrace_caller() in instrumented function
  */
 int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 		    unsigned long addr)
 {
 	unsigned long pc = rec->ip;
 	u32 old = 0, new;

 	if (!ftrace_find_callable_addr(rec, mod, &addr))
 		return -EINVAL;

 	old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
 	new = aarch64_insn_gen_nop();

 	return ftrace_modify_code(pc, old, new, true);
 }

 void arch_ftrace_update_code(int command)
 {
 	command |= FTRACE_MAY_SLEEP;
 	ftrace_modify_all_code(command);
 }
 #endif /* CONFIG_DYNAMIC_FTRACE */

 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 /*
  * function_graph tracer expects ftrace_return_to_handler() to be called
  * on the way back to parent. For this purpose, this function is called
  * in _mcount() or ftrace_caller() to replace return address (*parent) on
  * the call stack to return_to_handler.
  */
 void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
 			   unsigned long frame_pointer)
 {
 	unsigned long return_hooker = (unsigned long)&return_to_handler;
 	unsigned long old;

 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		return;

 	/*
 	 * Note:
 	 * No protection against faulting at *parent, which may be seen
 	 * on other archs. It's unlikely on AArch64.
 	 */
 	old = *parent;

 	if (!function_graph_enter(old, self_addr, frame_pointer,
 	    (void *)frame_pointer)) {
 		*parent = return_hooker;
 	}
 }

 #ifdef CONFIG_DYNAMIC_FTRACE

 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
 void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
 		       struct ftrace_ops *op, struct ftrace_regs *fregs)
 {
 	/*
 	 * When DYNAMIC_FTRACE_WITH_REGS is selected, `fregs` can never be NULL
 	 * and arch_ftrace_get_regs(fregs) will always give a non-NULL pt_regs
 	 * in which we can safely modify the LR.
 	 */
 	struct pt_regs *regs = arch_ftrace_get_regs(fregs);
 	unsigned long *parent = (unsigned long *)&procedure_link_pointer(regs);

 	prepare_ftrace_return(ip, parent, frame_pointer(regs));
 }
 #else
 /*
  * Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
  * depending on @enable.
  */
 static int ftrace_modify_graph_caller(bool enable)
 {
 	unsigned long pc = (unsigned long)&ftrace_graph_call;
 	u32 branch, nop;

 	branch = aarch64_insn_gen_branch_imm(pc,
 					     (unsigned long)ftrace_graph_caller,
 					     AARCH64_INSN_BRANCH_NOLINK);
 	nop = aarch64_insn_gen_nop();

 	if (enable)
 		return ftrace_modify_code(pc, nop, branch, true);
 	else
 		return ftrace_modify_code(pc, branch, nop, true);
 }

 int ftrace_enable_ftrace_graph_caller(void)
 {
 	return ftrace_modify_graph_caller(true);
 }

 int ftrace_disable_ftrace_graph_caller(void)
 {
 	return ftrace_modify_graph_caller(false);
 }
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 #endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* arch/arm64/kernel/ftrace.c
	*
	* Copyright (C) 2013 Linaro Limited
	* Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
	*/

	#include <linux/ftrace.h>
	#include <linux/module.h>
	#include <linux/swab.h>
	#include <linux/uaccess.h>

	#include <asm/cacheflush.h>
	#include <asm/debug-monitors.h>
	#include <asm/ftrace.h>
	#include <asm/insn.h>
	#include <asm/patching.h>

	#ifdef CONFIG_DYNAMIC_FTRACE
	/*
	* Replace a single instruction, which may be a branch or NOP.
	* If @validate == true, a replaced instruction is checked against 'old'.
	*/
	static int ftrace_modify_code(unsigned long pc, u32 old, u32 new,
	bool validate)
	{
	u32 replaced;

	/*
	* Note:
	* We are paranoid about modifying text, as if a bug were to happen, it
	* could cause us to read or write to someplace that could cause harm.
	* Carefully read and modify the code with aarch64_insn_*() which uses
	* probe_kernel_*(), and make sure what we read is what we expected it
	* to be before modifying it.
	*/
	if (validate) {
	if (aarch64_insn_read((void *)pc, &replaced))
	return -EFAULT;

	if (replaced != old)
	return -EINVAL;
	}
	if (aarch64_insn_patch_text_nosync((void *)pc, new))
	return -EPERM;

	return 0;
	}

	/*
	* Replace tracer function in ftrace_caller()
	*/
	int ftrace_update_ftrace_func(ftrace_func_t func)
	{
	unsigned long pc;
	u32 new;

	pc = (unsigned long)ftrace_call;
	new = aarch64_insn_gen_branch_imm(pc, (unsigned long)func,
	AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, 0, new, false);
	}

	static struct plt_entry get_ftrace_plt(struct module mod, unsigned long addr)
	{
	#ifdef CONFIG_ARM64_MODULE_PLTS
	struct plt_entry *plt = mod->arch.ftrace_trampolines;

	if (addr == FTRACE_ADDR)
	return &plt[FTRACE_PLT_IDX];
	if (addr == FTRACE_REGS_ADDR &&
	IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
	return &plt[FTRACE_REGS_PLT_IDX];
	#endif
	return NULL;
	}

	/*
	* Find the address the callsite must branch to in order to reach '*addr'.
	*
	* Due to the limited range of 'BL' instructions, modules may be placed too far
	* away to branch directly and must use a PLT.
	*
	* Returns true when '*addr' contains a reachable target address, or has been
	* modified to contain a PLT address. Returns false otherwise.
	*/
	static bool ftrace_find_callable_addr(struct dyn_ftrace *rec,
	struct module *mod,
	unsigned long *addr)
	{
	unsigned long pc = rec->ip;
	long offset = (long)*addr - (long)pc;
	struct plt_entry *plt;

	/*
	* When the target is within range of the 'BL' instruction, use 'addr'
	* as-is and branch to that directly.
	*/
	if (offset >= -SZ_128M && offset < SZ_128M)
	return true;

	/*
	* When the target is outside of the range of a 'BL' instruction, we
	* must use a PLT to reach it. We can only place PLTs for modules, and
	* only when module PLT support is built-in.
	*/
	if (!IS_ENABLED(CONFIG_ARM64_MODULE_PLTS))
	return false;

	/*
	* 'mod' is only set at module load time, but if we end up
	* dealing with an out-of-range condition, we can assume it
	* is due to a module being loaded far away from the kernel.
	*
	* NOTE: __module_text_address() must be called with preemption
	* disabled, but we can rely on ftrace_lock to ensure that 'mod'
	* retains its validity throughout the remainder of this code.
	*/
	if (!mod) {
	preempt_disable();
	mod = __module_text_address(pc);
	preempt_enable();
	}

	if (WARN_ON(!mod))
	return false;

	plt = get_ftrace_plt(mod, *addr);
	if (!plt) {
	pr_err("ftrace: no module PLT for %ps\n", (void )addr);
	return false;
	}

	*addr = (unsigned long)plt;
	return true;
	}

	/*
	* Turn on the call to ftrace_caller() in instrumented function
	*/
	int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
	{
	unsigned long pc = rec->ip;
	u32 old, new;

	if (!ftrace_find_callable_addr(rec, NULL, &addr))
	return -EINVAL;

	old = aarch64_insn_gen_nop();
	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, old, new, true);
	}

	#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
	int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
	unsigned long addr)
	{
	unsigned long pc = rec->ip;
	u32 old, new;

	if (!ftrace_find_callable_addr(rec, NULL, &old_addr))
	return -EINVAL;
	if (!ftrace_find_callable_addr(rec, NULL, &addr))
	return -EINVAL;

	old = aarch64_insn_gen_branch_imm(pc, old_addr,
	AARCH64_INSN_BRANCH_LINK);
	new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);

	return ftrace_modify_code(pc, old, new, true);
	}

	/*
	* The compiler has inserted two NOPs before the regular function prologue.
	* All instrumented functions follow the AAPCS, so x0-x8 and x19-x30 are live,
	* and x9-x18 are free for our use.
	*
	* At runtime we want to be able to swing a single NOP <-> BL to enable or
	* disable the ftrace call. The BL requires us to save the original LR value,
	* so here we insert a <MOV X9, LR> over the first NOP so the instructions
	* before the regular prologue are:
	*
	* \| Compiled \| Disabled \| Enabled \|
	* +----------+------------+------------+
	* \| NOP \| MOV X9, LR \| MOV X9, LR \|
	* \| NOP \| NOP \| BL <entry> \|
	*
	* The LR value will be recovered by ftrace_regs_entry, and restored into LR
	* before returning to the regular function prologue. When a function is not
	* being traced, the MOV is not harmful given x9 is not live per the AAPCS.
	*
	* Note: ftrace_process_locs() has pre-adjusted rec->ip to be the address of
	* the BL.
	*/
	int ftrace_init_nop(struct module mod, struct dyn_ftrace rec)
	{
	unsigned long pc = rec->ip - AARCH64_INSN_SIZE;
	u32 old, new;

	old = aarch64_insn_gen_nop();
	new = aarch64_insn_gen_move_reg(AARCH64_INSN_REG_9,
	AARCH64_INSN_REG_LR,
	AARCH64_INSN_VARIANT_64BIT);
	return ftrace_modify_code(pc, old, new, true);
	}
	#endif

	/*
	* Turn off the call to ftrace_caller() in instrumented function
	*/
	int ftrace_make_nop(struct module mod, struct dyn_ftrace rec,
	unsigned long addr)
	{
	unsigned long pc = rec->ip;
	u32 old = 0, new;

	if (!ftrace_find_callable_addr(rec, mod, &addr))
	return -EINVAL;

	old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
	new = aarch64_insn_gen_nop();

	return ftrace_modify_code(pc, old, new, true);
	}

	void arch_ftrace_update_code(int command)
	{
	command \|= FTRACE_MAY_SLEEP;
	ftrace_modify_all_code(command);
	}
	#endif /* CONFIG_DYNAMIC_FTRACE */

	#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	/*
	* function_graph tracer expects ftrace_return_to_handler() to be called
	* on the way back to parent. For this purpose, this function is called
	* in _mcount() or ftrace_caller() to replace return address (*parent) on
	* the call stack to return_to_handler.
	*/
	void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
	unsigned long frame_pointer)
	{
	unsigned long return_hooker = (unsigned long)&return_to_handler;
	unsigned long old;

	if (unlikely(atomic_read(&current->tracing_graph_pause)))
	return;

	/*
	* Note:
	* No protection against faulting at *parent, which may be seen
	* on other archs. It's unlikely on AArch64.
	*/
	old = *parent;

	if (!function_graph_enter(old, self_addr, frame_pointer,
	(void *)frame_pointer)) {
	*parent = return_hooker;
	}
	}

	#ifdef CONFIG_DYNAMIC_FTRACE

	#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
	void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
	struct ftrace_ops op, struct ftrace_regs fregs)
	{
	/*
	* When DYNAMIC_FTRACE_WITH_REGS is selected, `fregs` can never be NULL
	* and arch_ftrace_get_regs(fregs) will always give a non-NULL pt_regs
	* in which we can safely modify the LR.
	*/
	struct pt_regs *regs = arch_ftrace_get_regs(fregs);
	unsigned long parent = (unsigned long )&procedure_link_pointer(regs);

	prepare_ftrace_return(ip, parent, frame_pointer(regs));
	}
	#else
	/*
	* Turn on/off the call to ftrace_graph_caller() in ftrace_caller()
	* depending on @enable.
	*/
	static int ftrace_modify_graph_caller(bool enable)
	{
	unsigned long pc = (unsigned long)&ftrace_graph_call;
	u32 branch, nop;

	branch = aarch64_insn_gen_branch_imm(pc,
	(unsigned long)ftrace_graph_caller,
	AARCH64_INSN_BRANCH_NOLINK);
	nop = aarch64_insn_gen_nop();

	if (enable)
	return ftrace_modify_code(pc, nop, branch, true);
	else
	return ftrace_modify_code(pc, branch, nop, true);
	}

	int ftrace_enable_ftrace_graph_caller(void)
	{
	return ftrace_modify_graph_caller(true);
	}

	int ftrace_disable_ftrace_graph_caller(void)
	{
	return ftrace_modify_graph_caller(false);
	}
	#endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
	#endif /* CONFIG_DYNAMIC_FTRACE */
	#endif /* CONFIG_FUNCTION_GRAPH_TRACER */